The present invention relates to the field of document processing apparatus such as printers, copiers, document scanners, facsimile machines and other document processing and handling apparatus and devices and, more particularly, to apparatus and methods of detecting foreign objects such as paper clips, staples and the like which may inadvertently enter the document processing apparatus or its media feed path. The invention will be described with reference to an automatic document feeder (ADF) used in a multi-function document processing apparatus, but the details and concepts disclosed herein are broadly applicable to a much wider variety of equipment.
Optical and mechanical document load sensors have been used to detect (1) the presence (or absence) of a document sheet or other objects to be scanned in a document input or feed tray and (2) the presence (or absence) of the object or document sheet when it reaches a position at or near a scan line from which light directed onto the document sheet is reflected onto a scan module comprised of a plurality of light responsive elements, as is well known in the art. Optical and mechanical load sensors are also used to detect the presence of blank media sheets onto which copies are produced. Electrical output signals produced by optical and mechanical sheet sensors are used to control the feeding of blank media from a feed tray and document sheets, one at a time, from an ADF tray into the document processing apparatus and to control the beginning and ending of scanning.
Various systems have been devised for detecting the presence of paper clips, staples or other metallic objects that may be present in a document feed tray. One system uses an electrical field generator underlying the document tray where staples or clips are most likely to be found. Energization of the detector commences a period of time after the tray is loaded so as to avoid detection and production of signals caused by other metal objects that may be temporarily present when the tray is being loaded such as an operator""s ring or wristwatch.
A method and a simple apparatus for sensing the presence of a foreign metal object such as a metal paper clip or staple, and discriminating such objects from other metal objects such as rings and watches which are often present is desired. The apparatus should be capable of producing alarm or feeder control signals for automatically shutting down automatic sheet feeding of either or both of the document and blank media sheets into the document processor and be capable of fulfilling its intended function regardless of whether the sheets are fed by an ADF or manually.
Disclosed herein is a document processing method and a document processing apparatus that includes a feeder for transporting document sheets along a feed path; and a detector for detecting the presence of foreign metal objects in said feed path. The detector comprises a source of alternating electrical energy connected to a conductive transmitter loop for generating a pulsed magnetic field proximate the feed path and a conductive receiver loop that receives reflected magnetic field signals. The reflected magnetic signals induce electrical signals in the receiver loop which are amplified and processed to produce output signals which are sent to a phase shift analyzer which discriminates among output signals produced in the receiver loop by magnetic reflections from metal objects of varying types to provide an output signal when an undesired metal object in the feed path is detected.